1. Field of the Invention
This invention relates to an extensible level which can be elongated to extend the base of a level measurement, and which also can be separated into separately-useful level components in a range of sizes.
2. Description of the Prior Art
Carpenter's tools often include at least one level mechanism, normally a transparent curved tube or barrel-shaped tube filled with a liquid except for a bubble that seeks the highest point. Pendulum levels are known but are less common. The level, e.g. tube, is mounted on some form of a housing that is placed against a straight edge to be checked by viewing the bubble in the tube. The tube is mounted on the housing at a predetermined orientation relative to a flat reference edge of the housing. The flat reference edge is placed against a straight edge on a structural member such as a stud, doorjamb, etc., to be checked for correct alignment. While many hand tools such as try-square tools may have a level device built into them, a tool having a short housing for the level necessarily will be sensitive to short variations in linearity of the edge to be checked, and may not accurately reflect -the alignment of a member which is substantially longer than the housing of the level. For optimum accuracy, the flat edge of the level housing should have a length at least as long as the member to be checked. High quality carpenter's levels are often quite long, for example up to two meters in length. On the other hand, a level which is longer than the member to be checked is unnecessarily cumbersome. A variety of choices for lengths of the level are desirable, whereby for convenience and for checking short members a shorter level is available and for accuracy over the span of an elongated member a longer level can be used as well. Of course, the user is not interested in obtaining and maintaining a large number of tools which individually are only seldom used. Accordingly, there has been a need for a conveniently length-variable leveling tool to eliminate the need to carry several pieces of equipment while retaining convenience and full span.
Metrulis U.S. Pat. No. 3,522,657 and Conn U.S. Pat. No. 4,317,289 disclose extensible rule/level combinations which are pivotable at a hinge and therefore become longer when unfolded. However, the Conn device is extensible only to the extent of the length achieved when its parts are at 180 degrees to one another. Moreover, any pivotable level configuration is potentially inaccurate in that the respective segments may not be exactly co-linear when deployed for a measurement. The Metrulis device has pairs of level components pivoted together at their adjacent ends, with various arrangements as to positions available, including adjustable sections with 90 degree and 45 degree level tubes, and locking means for maintaining the selected position of the pivotable halves while the tool is being used in a particular position. These adjustments present the benefit of convenience as well as a possibility of error. Both of the devices shown in these references are intended as multi-function tools, for example being capable of functioning as squaring tools.
The standard configuration for a tool to be used only as a level (i.e., not a multi-function tool which happens to include a level) is similar to a straightedge. Straightedge rules are known that include levels and achieve extensibility for making length measurements by telescoping a graduated scale. Metrulis U.S. Pat. No. 3,522,657 shows both a hinging level and also a telescoping extensible scale or rule. Although extending the telescoping rule does extend the length of the entire device, such extending is not helpful as an extension of the effective length of the level. The extension is only useful as an extension of the scale or rule. This is true because the rule is narrower than the housing from which the rule telescopes and the edge of that housing is the flat edge to which the level indicating mechanism (e.g., spirit level) is referenced. The stepwise decrease in width precludes an extensible flat edge to be used in adjustable length leveling. Other similar devices are disclosed in Peterson et al., U.S. Pat. No. 4,099,331 and Jansson U.S. Pat. No. 4,399,616 in which rules are extensible from the ends of levels. These devices cannot be accurate as extensible levels because any reading is referenced to an uncertain line from the level housing to the extended rule end, which is not co-linear with the reference edge of the level housing.
Heater U.S. Pat. No. 3,762,058 is slightly different. This patent discloses a telescoping-scale measuring instrument which employs telescoping tubes or rods to provide for length measuring. In this case the device has the level mechanism disposed at the end of the smaller, extensible tube rather than on the wider housing In the same manner as above, however, a reading taken from end point to end point of the variably-extended rule will not be based on a non-varying line of reference.
While these previous patents disclose multiple-component pivoted or extensible tools having squaring, leveling, and/or measuring functions and are presumably effective for their respective intended uses, no previous device is characterized by an adjustably extensible level which has one or more level mechanisms referenced to a straight edge defined by co-linear edges of separable, separately useful level components in convenient lengths, does not fold, and which provides for level readings taken on the same line of reference at both ends of the level, regardless of the extent to which the device is extended.